It is shown that the Otto cycle, and more efficient extended expansion cycles, can be modified to use regenerative heat exchange. The heat exchange is beneficial because it reduces the pressure and volume needed for a given efficiency or equivalently it increases the efficiency which can be achieved within the same pressure and volume limitations.
STIRLING ENGINES use regenerators to span the temperature difference between the isothermal heating and cooling phases of their thermodynamic cycle. Recently it has been proposed (1,2)* that regenerators could be used in internal combustion engines. This note summarises the incentives for applying heat exchange in a variety of idealised perfect gas cycles.